The invention relates to a method and system for inserting a fiber optical sensing cable into an underwater well, such as a subsea well.
It is known to insert an optical fiber into a guide tube in an oil and/or gas production well from a fixed platform to monitor the influx profile along the length of the inflow zone of the well. The optical fiber may use the Raman and/or Brillouin effect along the length of the fiber to monitor the temperature and/or pressure distribution along the length of the guide tube, from which information can be derived about the flux, density and/or composition of the well effluents, which may comprise a mixture of crude oil, water and natural gas.
The optical fiber may be pumped into a U-shaped guide tube by a pumping unit which pumps fluid into an upper end of the guide tube, such that the fluid flowing through the guide tube pulls or drags the optical fiber through the guide tube. Each of the upper fiber ends is then, at the surface, manually spliced to the measurement system.
The known fiber installation techniques are not suitable for installation of fiber optical sensing systems in subsea wells via subsea wellheads due to the complexity of handling and pumping the optical fiber, stripping, cleaning and splicing the fiber(s) to the measurement system.
A currently available option to deploy the fiber in a subsea well is to attach a fixed cable in the well at the time of the completion. For wells with an upper/lower completion, wet-mateable fiber optic connectors for downhole use are required, which significantly adds to the cost and complexity with additional expensive rig time.
It is an object of the present invention to provide a method and system for inserting a fiber optical sensing cable into an underwater well in an efficient manner, without requiring the use of an offshore working rig or the presence of a floating or standing offshore platform above the well.